Billions of Years of Evolution Part 2

As Psions of Psionic Circles and citizens we should know the basic facts regarding the Earth and its properties as well as the history of its inhabitants. So let us continue with a brief account of some of the major…

As Psions of Psionic Circles and citizens we should know the basic facts regarding the Earth and its properties as well as the history of its inhabitants. So let us continue with a brief account of some of the major evolutionary changes in life from the beginning to current year.  

Introduction

Original Date:  September 9 2021

Last Updated: September 9 2021

Planet Earth Evolution Continued

We last discussed the facts.  Our planet earth has undergone many changes on the surface of the planet and in the atmosphere over its billions of years of existence. And during the last billions of years it has become the home of all plant and animal species that have been able to survive the multitude of changes that has occurred.  It is also the the home of 7.8 billions of human beings spread over 7 continents and thousands of islands.

As Psions and citizens we should know the basic facts regarding the Earth and its properties as well as the history of its inhabitants. So let us continue with the purpose of giving a brief account of some of the major evolutionary changes in life from the beginning to current year.     .

Let us start with recapitulating 2.9 billions ago to 2.0 billion years ago and move on from there.

2.9 billion years ago to 2.0 billion years ago

• The “great oxidation event”.  The poisonous waste produced by photosynthetic cyanobacteria – oxygen – starts to build up in the atmosphere. Dissolved oxygen makes the iron in the oceans “rust” and sink to the seafloor, forming striking banded iron formations.
• Yet others think that cyanobacteria began pumping out oxygen as early as 2.1 billion years ago, but that oxygen began to accumulate only due to some other factor, possibly a decline in methane-producing bacteria. Methane reacts with oxygen, removing it from the atmosphere, so fewer methane-belching bacteria would allow oxygen to build up.
• Earth freezes over in what may have been the first “snowball Earth”, possibly as a result of a lack of volcanic activity. When the ice eventually melts, it indirectly leads to more oxygen being released into the atmosphere.
• First undisputed fossil evidence of cyanobacteria, and of photosynthesis: the ability to take in sunlight and carbon dioxide, and obtain energy, releasing oxygen as a by-product.
• There is some evidence for an earlier date for the beginning of photosynthesis, but it has been called into question.
• Eukaryotic cells – cells with internal “organs” (known as organelles) – come into being. One key organelle is the nucleus: the control centre of the cell, in which the genes are stored in the form of DNA.
• Eukaryotic cells evolved when one simple cell engulfed another, and the two lived together, more or less amicably – an example of “endosymbiosis”. The engulfed bacteria eventually become mitochondria, which provide eukaryotic cells with energy. The last common ancestor of all eukaryotic cells had mitochondria – and had also developed sexual reproduction.
• Later, eukaryotic cells engulfed photosynthetic bacteria and formed a symbiotic relationship with them. The engulfed bacteria evolved into chloroplasts: the organelles that give green plants their colour and allow them to extract energy from sunlight.
• Different lineages of eukaryotic cells acquired chloroplasts in this way on at least three separate occasions, and one of the resulting cell lines went on to evolve into all green algae and green plants.

1.9 billion years ago to 1.0 billion years ago

• The eukaryotes divide into three groups: the ancestors of modern plants, fungi and animals split into separate lineages, and evolve separately. We do not know in what order the three groups broke with each other. At this time they were probably all still single-celled organisms.
• The first multicellular life develops around this time.

999 million years ago to 

• It is unclear exactly how or why this happens, but one possibility is that single-celled organisms go through a stage similar to that of modern choanoflagellates: single-celled creatures that sometimes form colonies consisting of many individuals. Of all the single-celled organisms known to exist, choanoflagellates are the most closely related to multicellular animals, lending support to this theory.
• The early multicellular animals undergo their first splits. First they divide into, essentially, the sponges and everything else – the latter being more formally known as the Eumetazoa.
• Around 20 million years later, a small group called the placozoa breaks away from the rest of the Eumetazoa. Placozoa are thin plate-like creatures about 1 millimetre across, and consist of only three layers of cells. It has been suggested that they may actually be the last common ancestor of all the
• The planet freezes over again in another “snowball Earth“.
• The comb jellies (ctenophores) split from the other multicellular animals. Like the cnidarians that will soon follow, they rely on water flowing through their body cavities to acquire oxygen and food.
• The ancestor of cnidarians (jellyfish and their relatives) breaks away from the other animals – though there is as yet no fossil evidence of what it looks like.
• Around this time, some animals evolve bilateral symmetry for the first time: that is, they now have a defined top and bottom, as well as a front and back.
• Little is known about how this happened. However, small worms called Acoela may be the closest surviving relatives of the first ever bilateral animal. It seems likely that the first bilateral animal was a kind of worm. Vernanimalcula guizhouena, which dates from around 600 million years ago, may be the earliest bilateral animal found in the fossil record.
• The Bilateria, those animals with bilateral symmetry, undergo a profound evolutionary split. They divide into the protostomes and deuterostomes.
• The deuterostomes eventually include all the vertebrates, plus an outlier group called the Ambulacraria. The protostomes become all the arthropods (insects, spiders, crabs, shrimp and so forth), various types of worm, and the microscopic rotifers.
• Neither may seem like an obvious “group”, but in fact the two can be distinguished by the way their embryos develop. The first hole that the embryo acquires, the blastopore, forms the anus in deuterostomes, but in protostomes it forms the mouth.
• The earliest known fossils of cnidarians, the group that includes jellyfish, sea anemones and corals, date to around this time – though the fossil evidence has been disputed.
• A small group breaks away from the main group of deuterostomes, known as the Ambulacraria. This group eventually becomes the echinoderms (starfish, brittle stars and their relatives) and two worm-like families called the hemichordates and Xenoturbellida.
• Another echinoderm, the sea lily, is thought to be the “missing link” between vertebrates (animals with backbones) and invertebrates (animals without backbones), a split that occurred around this time.
• As the first chordates – animals that have a backbone, or at least a primitive version of it – emerge among the deuterostomes, a surprising cousin branches off.
• The sea squirts (tunicates) begin their history as tadpole-like chordates, but metamorphose partway through their lives into bottom-dwelling filter feeders that look rather like a bag of seawater anchored to a rock. Their larvae still look like tadpoles today, revealing their close relationship to backboned animals.

• The Cambrian explosion begins, with many new body layouts appearing on the scene – though the seeming rapidity of the appearance of new life forms may simply be an illusion caused by a lack of older fossils.
• The first true vertebrate – an animal with a backbone – appears. It probably evolves from a jawless fish that has a notochord, a stiff rod of cartilage, instead of a true backbone. The first vertebrate is probably quite like a lamprey, hagfish or lancelet.
• Around the same time, the first clear fossils of trilobites appear. These invertebrates, which look like oversized woodlice and grow to 70 centimetres in length, proliferate in the oceans for the next 200 million years.
• Fish split into two major groups: the bony fish and cartilaginous fish. The cartilaginous fish, as the name implies, have skeletons made of cartilage rather than the harder bone. They eventually include all the sharks, skates and rays.
• The first four-legged animals, or tetrapods, evolve from intermediate species such as Tiktaalik, probably in shallow freshwater habitats.
• The first major split occurs in the tetrapods, with the amphibians branching off from the others.
• Within the remaining tetrapods, the sauropsids and synapsids split from one another. The sauropsids include all the modern reptiles, plus the dinosaurs and birds. The first synapsids are also reptiles, but have distinctive jaws. They are sometimes called “mammal-like reptiles”, and eventually evolve into the mammals.
• The pelycosaurs, the first major group of synapsid animals, dominate the land. The most famous example is Dimetrodon, a large predatory “reptile” with a sail on its back. Despite appearances, Dimetrodon is not a dinosaur.
• The therapsids, close cousins of the pelycosaurs, evolve alongside them and eventually replace them. The therapsids survive until the early Cretaceous, 100 million years ago. Well before that, a group of them called the cynodonts develops dog-like teeth and eventually evolves into the first mammals.

• The Permian period ends with the greatest mass extinction in Earth’s history, wiping out great swathes of species, including the last of the trilobites.
• As the ecosystem recovers, it undergoes a fundamental shift. Whereas before the synapsids (first the pelycosaurs, then the therapsids) dominated, the sauropsids now take over – most famously, in the form of dinosaurs. The ancestors of mammals survive as small, nocturnal creatures.
• In the oceans, the ammonites, cousins of the modern nautilus and octopus, evolve around this time. Several groups of reptiles colonise the seas, developing into the great marine reptiles of the dinosaur era.
• Bird-like footprints and a badly-preserved fossil called Protoavis suggest that some early dinosaurs are already evolving into birds at this time. This claim remains controversial.

• As the Triassic period comes to an end, another mass extinction strikes, paving the way for the dinosaurs to take over from their sauropsid cousins.
• Around the same time, proto-mammals evolve warm-bloodedness – the ability to maintain their internal temperature, regardless of the external conditions.
• The first split occurs in the early mammal population. The monotremes, a group of mammals that lay eggs rather than giving birth to live young, break apart from the others. Few monotremes survive today: they include the duck-billed platypus and the echidnas.
• A half-feathered, flightless dinosaur called Epidexipteryx, which may be an early step on the road to birds, lives in China.
• Archaeopteryx, the famous “first bird”, lives in Europe.
• Around this time, placental mammals split from their cousins the marsupials. These mammals, like the modern kangaroo, that give birth when their young are still very small, but nourish them in a pouch for the first few weeks or months of their lives.
• The majority of modern marsupials live in Australia, but they reach it by an extremely roundabout route. Arising in south-east Asia, they spread into north America (which was attached to Asia at the time), then to south America and Antarctica, before making the final journey to Australia about 50 million years ago.
• Eoconfuciusornis, a bird rather more advanced than Archaeopteryx, lives in China.
• The first flowering plants emerge, following a period of rapid evolution.The placental mammals split into their four major groups: the laurasiatheres (a hugely diverse group including all the hoofed mammals, whales, bats, and dogs), euarchontoglires (primates, rodents and others), Xenarthra (including anteaters and armadillos) and afrotheres (elephants, aardvarks and others). Quite how these splits occurred is unclear at present.

100 million years to 2 million years ago

• The Cretaceous dinosaurs reach their peak in size. The giant sauropod Argentinosaurus, believed to be the largest land animal in Earth’s history, lives around this time.
• The oceans become starved of oxygen, possibly due to a huge underwater volcanic eruption. Twenty-seven per cent of marine invertebrates are wiped out.
• The ancestors of modern primates split from the ancestors of modern rodents and lagomorphs (rabbits, hares and pikas). The rodents go on to be astonishingly successful, eventually making up around 40 per cent of modern mammal species.
• Grasses evolve – though it will be several million years before the vast open grasslands appear.

• The Cretaceous-Tertiary (K/T) extinction wipes out a swathe of species, including all the giant reptiles: the dinosaurs, pterosaurs, ichthyosaurs and plesiosaurs. The ammonites are also wiped out. The extinction clears the way for the mammals, which go on to dominate the planet.
• The primates split into two groups, known as the haplorrhines (dry-nosed primates) and the strepsirrhines (wet-nosed primates). The strepsirrhines eventually become the modern lemurs and aye-ayes, while the haplorrhines develop into monkeys and apes – and humans.
• The tarsier, a primate with enormous eyes to help it see at night, splits from the rest of the haplorrhines: the first to do so.

• The Palaeocene/Eocene extinction. A sudden rise in greenhouse gases sends temperatures soaring and transforms the planet, wiping out many species in the depths of the sea – though sparing species in shallow seas and on land.
• Artiodactyls, which look like a cross between a wolf and a tapir, begin evolving into whales.
• Indohyus, another possible ancestor of whales and dolphins, lives in India.
• The famous fossilized primate known as “Ida” lives in northern Europe. Early whales called protocetids live in shallow seas, returning to land to give birth.
• New World monkeys become the first simians (higher primates) to diverge from the rest of the group, colonizing South America.
• Apes split from the Old World monkeys.
• Gibbons become the first ape to split from the others.
• Orangutans branch off from the other great apes, spreading across southern Asia while their cousins remain in Africa.
• Gorillas branch off from the other great apes.

• Humans diverge from their closest relatives; the chimpanzees and bonobos.
• Shortly afterwards, hominins begin walking on two legs. See our interactive timeline of human evolution for the full story of how modern humans developed.
• A 700-kilogram rodent called Josephoartigasia monesi lives in South America. It is the largest rodent known to have lived, displacing the previous record holder: a giant guinea pig.

Well that takes us to just before the Quaternary Period

We have approximately 2 million to go until we are at current time.

To be continued next time.

Thanks for Reading!

Page 42.2

Copyright 2019-2024 Sabrina Renee Lemire